The disposal of plastic wastes is recently an issue of concern. Incineration and landfill are major methods for disposing of plastic wastes, however, incineration accelerates global warming while a decrease in the amount of land being reclaimed is a problem related with landfill disposal. Therefore, biodegrading methods are attracting attention. Polylactide resins have biodegradability and the development of various applications as next-generation plastics is in progress. In the near future, however, as with currently used plastics, a focus on the issue of wastes is strongly expected.
Polylactide resins are polymers that are hydrolyzed in a water system and are currently employed as medical and pharmaceutical materials. Since polylactide resins can be synthesized through lactic acid fermentation from regeneratable resources such as starch, they are attracting attention as a material for biodegradable plastics to replace general-purpose plastics for which environmental degradation is difficult. Polylactic resins are classified into poly-L-lactic acid, poly-D-lactic acid, poly-DL-lactic acid, and a copolymer with other polymers, depending on the type of constitutive monomer.
It is known that an enzyme accelerates hydrolysis of polylactide resins. An enzyme for degrading polylactide resins may be a hydrolase similar to protease, lipase, or esterase, although it is not yet specified. Further, until now microorganisms for directly biodegrading polylactide resins and wastes thereof and degradation method techniques using those microorganisms have been limited to the following: the actinomycetes Amycolatopsis mediterranei (FERM P-14921), Actinomadura viridis (FERM P-16247), and Streptomyces spp. (FERM P-15869, FERM P-15870); and the bacteria Staphylococcus hominis (FERM P-15867), Staphylococcus epidermidis (FERM P-15868), Bacillus subtilis (FERM P-16181), Bacillus circullans (FERM P-16182), and Bacillus stearothermophilus (FERM P-16183), and degradation using those bacteria. Thus, it can be said that investigation of techniques for actively degrading polylactide resins has not yet been sufficiently conducted.
The object of the present invention is, therefore, to provide novel microorganisms for directly biodegrading polylactide resins and plastics containing the same and a method therefor.